How to Manage Pests
UC Pest Management Guidelines
Pathogen: Alternaria alternata
(Reviewed 12/13, updated 12/13)
In this Guideline:
Blackmold is characterized by obvious lesions that appear on the surface of ripe fruit. Lesions are light to dark brown and vary from small flecks affecting only epidermal tissue to large, more or less circular, sunken lesions with decay extending into the carpel wall and often into the seed locule. During warm, humid weather the fungus may sporulate to form a black, velvetlike layer on the surface of the sunken lesions.
Comments on the Disease
Blackmold is a disease of ripe tomato fruit that appears in the field after rain or dew. Disease incidence is higher with increased late-season rain; it is most common in late-season processing tomatoes. Fungal spores need 3 to 5 hours of wetness to germinate. After germination they can infect fruit by directly penetrating the epidermis. A crop can be heavily damaged within 4 to 5 days following a period of rain and high humidity. The fungus also readily colonizes any wounds on the fruit, including sunburned areas.
Cultural practices help reduce the damage potential of the blackmold fungus but preventive treatments may be needed for control in areas where it poses a continual problem.
Cultural practices that encourage dense leaf canopies and the selection of varieties that develop and retain a heavy canopy, may aid in preventing blackmold by protecting fruit from dew. However, a dense canopy also retains high humidity that favors other fruit molds such as gray mold.
Organically Acceptable Methods
Cultural control is acceptable for use on organically certified produce.
Treatments are most likely necessary in late-harvest fields, in rainy years, or if the fruit is damaged. Apply the first treatment 4 to 6 weeks before anticipated harvest. Two applications may be necessary if harvest is anticipated after mid-September. Check with tomato processor representatives concerning allowed fungicides and rates.
UC IPM Pest Management Guidelines: Tomato
R. M. Davis, Plant Pathology, UC Davis